Eureka 的 Application Client 客户端的运行示例

上篇以一个 demo 示例介绍了 Eureka 的 Application Service 客户端角色。今天我们继续了解 Eureka 的 Application Client 客户端，以一个简单的交互示例，介绍 Application Client 是如何使用 Eureka 获取 Application Service 实例并发送请求的。
        上篇《 Eureka 的 Application Service 客户端的注册以及运行示例 》使用了一个 Socket 服务做为 demo，本文示例配合该文，将以一个 Socket 客户端对该服务进行请求。
         1. Eureka 服务器启动
        本文 demo 要求 Eureka Server 已经部署好，并已经启动。关于架设步骤参考博客《 Linux 下 Eureka 服务器的部署 》。
         2. Application Service 服务启动
        直接将《 Eureka 的 Application Service 客户端的注册以及运行示例 》中的小 demo 跑起来(Socket Server 启动，开始侍服网络请求)。
         3. Application Client 配置文件的编写
        我们的 Application Client 就用官方提供  demo  里的 sampleclient 下的 sample-eureka-client.properties 即可，当然还要根据实际情况修正一下，比如把 eureka.serviceUrl.default(默认情况下本客户端将要注册到的 Eureka 服务器)： http://serverIP:8080/eureka/v2/ ：

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1. ###Eureka Client configuration for Sample Eureka Client  
2.   
3.   
4. #Properties based configuration for eureka client. The properties specified here is mostly what the users  
5. #need to change. All of these can be specified as a java system property with -D option (eg)-Deureka.region=us-east-1  
6. #For additional tuning options refer <url to go here>  
7.   
8.   
9.   
10.   
11. #Region where eureka is deployed -For AWS specify one of the AWS regions, for other datacenters specify a arbitrary string  
12. #indicating the region.This is normally specified as a -D option (eg) -Deureka.region=us-east-1  
13. eureka.region=default  
14.   
15.   
16. #Name of the application to be identified by other services  
17.   
18.   
19. eureka.name=sampleEurekaClient  
20.   
21.   
22. #Virtual host name by which the clients identifies this service  
23. #eureka.vipAddress=eureka.mydomain.net  
24.   
25.   
26. #The port where the service will be running and servicing requests  
27. #eureka.port=80  
28.   
29.   
30. #For eureka clients running in eureka server, it needs to connect to servers in other zones  
31. eureka.preferSameZone=true  
32.   
33.   
34. #Change this if you want to use a DNS based lookup for determining other eureka servers. For example  
35. #of specifying the DNS entries, check the eureka-client-test.properties, eureka-client-prod.properties  
36. eureka.shouldUseDns=false  
37.   
38.   
39. eureka.us-east-1.availabilityZones=default  
40.   
41.   
42. eureka.serviceUrl.default=http://serverIP:8080/eureka/v2/  

         4. 日志配置
        就用官方提供  demo  里的 sampleclient 下的 log4j.properties 即可，当然还要根据实际需要修正一下，比如给 com.netflix.eureka 包的输出级别设置为 DEBUG(log4j.properties 追加 log4j.logger.com.netflix.eureka=DEBUG)，以方便我们研发期跟踪调试。

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1. log4j.rootCategory=INFO,stdout  
2. log4j.appender.stdout=org.apache.log4j.ConsoleAppender  
3. log4j.appender.stdout.layout=org.apache.log4j.PatternLayout  
4. log4j.appender.stdout.layout.ConversionPattern=%d %-5p %C:%L [%t] [%M] %m%n  
5. log4j.logger.com.netflix.eureka=DEBUG  

         5. 寻找本次请求的 Application Service 实例
        客户端在向 Application Service 请求之前得先从 Eureka Server 拿到侍服本次请求的 Application Service 实例。寻找本次请求的 Application Service 实例的代码如下：

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1. // Register with Eureka  
2. DiscoveryManager.getInstance().initComponent(  
3.         new MyDataCenterInstanceConfig(),  
4.         new DefaultEurekaClientConfig());  
5. ApplicationInfoManager.getInstance().setInstanceStatus(  
6.         InstanceStatus.UP);  
7. String vipAddress = configInstance.getStringProperty(  
8.         "eureka.vipAddress", "sampleservice.mydomain.net").get();  
9. InstanceInfo nextServerInfo = DiscoveryManager.getInstance()  
10.         .getDiscoveryClient()  
11.         .getNextServerFromEureka(vipAddress, false);  

        第一句初始化本客户端，第二句告诉 Eureka 本客户端处于就绪状态，接下来两句是使用 Eureka 找到对本次请求进行侍服的 Application Service 实例。
         6. Application Client 网络请求
        Application Client 拿到 Application Service 之后立马进行网络 Socket 请求，进行数据信息交互。

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1. Socket s = new Socket();  
2. int serverPort = nextServerInfo.getPort();  
3. try {  
4.     s.connect(new InetSocketAddress(nextServerInfo.getHostName(),  
5.             serverPort));  
6. } catch (IOException e) {  
7.     System.err.println("Could not connect to the server :"  
8.             + nextServerInfo.getHostName() + " at port " + serverPort);  
9. }  
10. try {  
11.     System.out.println("Connected to server. Sending a sample request");  
12.     PrintStream out = new PrintStream(s.getOutputStream());  
13.     out.println("Sample request " + new Date());  
14.     String str = null;  
15.     System.out.println("Waiting for server response..");  
16.     BufferedReader rd = new BufferedReader(new InputStreamReader(  
17.             s.getInputStream()));  
18.     str = rd.readLine();  
19.     if (str != null) {  
20.         System.out  
21.                 .println("Received response from server. Communication all fine using Eureka :");  
22.         System.out.println("Exiting the client. Demo over..");  
23.     }  
24.     rd.close();  
25. } catch (IOException e) {  
26.     e.printStackTrace();  
27. }  

         7. Application Client 关闭时取消注册
        Application Client 在关闭时要将自己在 Eureka 的注册取消掉。

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1. public void unRegisterWithEureka() {  
2.     // Un register from eureka.  
3.     DiscoveryManager.getInstance().shutdownComponent();  
4. }  

         8. 运行 demo
        新建一个项目(不要和 Application Service 的 demo 跑在同一个项目下)，现在我们把完整的 Application Client 代码整理一下。

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1. /* 
2.  * Copyright 2012 Netflix, Inc. 
3.  * 
4.  *    Licensed under the Apache License, Version 2.0 (the "License"); 
5.  *    you may not use this file except in compliance with the License. 
6.  *    You may obtain a copy of the License at 
7.  * 
8.  *        http://www.apache.org/licenses/LICENSE-2.0 
9.  * 
10.  *    Unless required by applicable law or agreed to in writing, software 
11.  *    distributed under the License is distributed on an "AS IS" BASIS, 
12.  *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 
13.  *    See the License for the specific language governing permissions and 
14.  *    limitations under the License. 
15.  */  
16.   
17.   
18. package com.netflix.eureka;  
19.   
20.   
21. import java.io.BufferedReader;  
22. import java.io.IOException;  
23. import java.io.InputStreamReader;  
24. import java.io.PrintStream;  
25. import java.net.InetSocketAddress;  
26. import java.net.Socket;  
27. import java.util.Date;  
28.   
29.   
30. import org.slf4j.Logger;  
31. import org.slf4j.LoggerFactory;  
32.   
33.   
34. import com.netflix.appinfo.ApplicationInfoManager;  
35. import com.netflix.appinfo.InstanceInfo;  
36. import com.netflix.appinfo.InstanceInfo.InstanceStatus;  
37. import com.netflix.appinfo.MyDataCenterInstanceConfig;  
38. import com.netflix.config.DynamicPropertyFactory;  
39. import com.netflix.discovery.DefaultEurekaClientConfig;  
40. import com.netflix.discovery.DiscoveryManager;  
41.   
42.   
43. /** 
44.  * Sample Eureka client that discovers the service using Eureka and sends 
45.  * requests. 
46.  * 
47.  * @author Karthik Ranganathan 
48.  * 
49.  */  
50. public class SampleEurekaClient {  
51.     private static final DynamicPropertyFactory configInstance = com.netflix.config.DynamicPropertyFactory  
52.             .getInstance();  
53.       
54.     private static final Logger logger = LoggerFactory  
55.     .getLogger(SampleEurekaClient.class);  
56.   
57.   
58.     public void sendRequestToServiceUsingEureka() {  
59.         // Register with Eureka  
60.         DiscoveryManager.getInstance().initComponent(  
61.                 new MyDataCenterInstanceConfig(),  
62.                 new DefaultEurekaClientConfig());  
63.         ApplicationInfoManager.getInstance().setInstanceStatus(  
64.                 InstanceStatus.UP);  
65.         String vipAddress = configInstance.getStringProperty(  
66.                 "eureka.vipAddress", "sampleservice.mydomain.net").get();  
67.         InstanceInfo nextServerInfo = DiscoveryManager.getInstance()  
68.                 .getDiscoveryClient()  
69.                 .getNextServerFromEureka(vipAddress, false);  
70.   
71.   
72.         Socket s = new Socket();  
73.         int serverPort = nextServerInfo.getPort();  
74.         try {  
75.             s.connect(new InetSocketAddress(nextServerInfo.getHostName(),  
76.                     serverPort));  
77.         } catch (IOException e) {  
78.             System.err.println("Could not connect to the server :"  
79.                     + nextServerInfo.getHostName() + " at port " + serverPort);  
80.         }  
81.         try {  
82.             System.out.println("Connected to server. Sending a sample request");  
83.             PrintStream out = new PrintStream(s.getOutputStream());  
84.             out.println("Sample request " + new Date());  
85.             String str = null;  
86.             System.out.println("Waiting for server response..");  
87.             BufferedReader rd = new BufferedReader(new InputStreamReader(  
88.                     s.getInputStream()));  
89.             str = rd.readLine();  
90.             if (str != null) {  
91.                 System.out  
92.                         .println("Received response from server. Communication all fine using Eureka :");  
93.                 System.out.println("Exiting the client. Demo over..");  
94.             }  
95.             rd.close();  
96.         } catch (IOException e) {  
97.             e.printStackTrace();  
98.         }  
99.         this.unRegisterWithEureka();  
100.     }  
101.   
102.   
103.     public void unRegisterWithEureka() {  
104.         // Un register from eureka.  
105.         DiscoveryManager.getInstance().shutdownComponent();  
106.     }  
107.   
108.   
109.     public static void main(String[] args) {  
110.         SampleEurekaClient sampleEurekaService = new SampleEurekaClient();  
111.         sampleEurekaService.sendRequestToServiceUsingEureka();  
112.   
113.   
114.     }  
115.   
116.   
117. }  

        如上篇博客所述一样把各种依赖包加进本文 demo 的 CLASSPATH，然后把第三、四步写好的 sample-eureka-client.properties、log4j.properties 也拷贝进 CLASSPATH，并将 sample-eureka-client.properties 重命名为 config.properties(原因参考上篇博客)，接下来就可以运行本文 demo 了。run SampleEurekaClient，日志结果如下：
2014-07-10 11:02:51,860 INFO  com.netflix.config.sources.URLConfigurationSource:125 [main] [<init>] URLs to be used as dynamic configuration source: [file:/D:/javaprojects/test2/bin/config.properties]
2014-07-10 11:02:51,927 INFO  com.netflix.config.DynamicPropertyFactory:281 [main] [getInstance] DynamicPropertyFactory is initialized with configuration sources: com.netflix.config.ConcurrentCompositeConfiguration@5ca46701
2014-07-10 11:02:52,060 WARN  com.netflix.appinfo.PropertiesInstanceConfig:349 [main] [init] Cannot find the properties specified : eureka-client. This may be okay if there are other environment specific properties or the configuration is installed with a different mechanism.
2014-07-10 11:02:52,065 WARN  com.netflix.discovery.DefaultEurekaClientConfig:95 [main] [init] Cannot find the properties specified : eureka-client. This may be okay if there are other environment specific properties or the configuration is installed with a different mechanism.
2014-07-10 11:02:52,103 INFO  com.netflix.appinfo.providers.EurekaConfigBasedInstanceInfoProvider:79 [main] [get] Setting initial instance status as: STARTING
2014-07-10 11:02:53,667 INFO  com.netflix.discovery.DiscoveryClient:646 [main] [fetchRegistry] Disable delta property : false
2014-07-10 11:02:53,667 INFO  com.netflix.discovery.DiscoveryClient:647 [main] [fetchRegistry] Single vip registry refresh property : null
2014-07-10 11:02:53,667 INFO  com.netflix.discovery.DiscoveryClient:648 [main] [fetchRegistry] Force full registry fetch : false
2014-07-10 11:02:53,667 INFO  com.netflix.discovery.DiscoveryClient:649 [main] [fetchRegistry] Application is null : false
2014-07-10 11:02:53,667 INFO  com.netflix.discovery.DiscoveryClient:650 [main] [fetchRegistry] Registered Applications size is zero : true
2014-07-10 11:02:53,668 INFO  com.netflix.discovery.DiscoveryClient:652 [main] [fetchRegistry] Application version is -1: true
2014-07-10 11:02:54,061 INFO  com.netflix.discovery.DiscoveryClient:992 [main] [makeRemoteCall] Finished a call to service url http://serverIP:8080/eureka/v2/ and url path apps/ with status code 200.
2014-07-10 11:02:54,061 INFO  com.netflix.discovery.DiscoveryClient:758 [main] [getAndStoreFullRegistry] Getting all instance registry info from the eureka server
2014-07-10 11:02:54,568 INFO  com.netflix.discovery.DiscoveryClient:765 [main] [getAndStoreFullRegistry] The response status is 200
2014-07-10 11:02:54,578 INFO  com.netflix.discovery.DiscoveryClient:1056 [main] [initScheduledTasks] Starting heartbeat executor: renew interval is: 30
Connected to server. Sending a sample request
Waiting for server response..
Received response from server. Communication all fine using Eureka :
Exiting the client. Demo over..
        证明 demo 获取 Application Service 实例并请求成功。
        可以看出，Application Service 实例的信息都封装在了 com.netflix.appinfo.InstanceInfo 下，那么我们还能从中获取哪些信息？SampleEurekaClient 类加入以下代码：

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1. logger.debug("nextServerInfo.getAppGroupName()-" + nextServerInfo.getAppGroupName());  
2. logger.debug("nextServerInfo.getAppName()-" + nextServerInfo.getAppName());  
3. logger.debug("nextServerInfo.getASGName()-" + nextServerInfo.getASGName());  
4. logger.debug("nextServerInfo.getHomePageUrl()-" + nextServerInfo.getHomePageUrl());  
5. logger.debug("nextServerInfo.getHostName()-" + nextServerInfo.getHostName());  
6. logger.debug("nextServerInfo.getId()-" + nextServerInfo.getId());  
7. logger.debug("nextServerInfo.getIPAddr()-" + nextServerInfo.getIPAddr());  
8. logger.debug("nextServerInfo.getLastUpdatedTimestamp()-" + nextServerInfo.getLastUpdatedTimestamp());  
9. logger.debug("nextServerInfo.getPort()-" + nextServerInfo.getPort());  
10. logger.debug("nextServerInfo.getSecureVipAddress()-" + nextServerInfo.getSecureVipAddress());  
11. logger.debug("nextServerInfo.getStatusPageUrl()-" + nextServerInfo.getStatusPageUrl());  
12. logger.debug("nextServerInfo.getVIPAddress()-" + nextServerInfo.getVIPAddress());  
13. logger.debug("nextServerInfo.getLastDirtyTimestamp()-" + nextServerInfo.getLastDirtyTimestamp());  
14. logger.debug("nextServerInfo.getHealthCheckUrls()-" + nextServerInfo.getHealthCheckUrls());  
15. logger.debug("nextServerInfo.getStatus()-" + nextServerInfo.getStatus());  

        然后重新运行本文 demo，以上语句打印结果如下：
2014-07-10 11:02:54,619 DEBUG com.netflix.eureka.SampleEurekaClient:69 [main] [sendRequestToServiceUsingEureka] nextServerInfo.getAppGroupName()-UNKNOWN
2014-07-10 11:02:54,619 DEBUG com.netflix.eureka.SampleEurekaClient:70 [main] [sendRequestToServiceUsingEureka] nextServerInfo.getAppName()-SAMPLESERVICE
2014-07-10 11:02:54,619 DEBUG com.netflix.eureka.SampleEurekaClient:71 [main] [sendRequestToServiceUsingEureka] nextServerInfo.getASGName()-null
2014-07-10 11:02:54,619 DEBUG com.netflix.eureka.SampleEurekaClient:72 [main] [sendRequestToServiceUsingEureka] nextServerInfo.getHomePageUrl()-http://defonds-win7:1935/
2014-07-10 11:02:54,620 DEBUG com.netflix.eureka.SampleEurekaClient:73 [main] [sendRequestToServiceUsingEureka] nextServerInfo.getHostName()-defonds-win7
2014-07-10 11:02:54,620 DEBUG com.netflix.eureka.SampleEurekaClient:74 [main] [sendRequestToServiceUsingEureka] nextServerInfo.getId()-defonds-win7
2014-07-10 11:02:54,620 DEBUG com.netflix.eureka.SampleEurekaClient:75 [main] [sendRequestToServiceUsingEureka] nextServerInfo.getIPAddr()-172.21.40.134
2014-07-10 11:02:54,620 DEBUG com.netflix.eureka.SampleEurekaClient:76 [main] [sendRequestToServiceUsingEureka] nextServerInfo.getLastUpdatedTimestamp()-1404961202884
2014-07-10 11:02:54,620 DEBUG com.netflix.eureka.SampleEurekaClient:77 [main] [sendRequestToServiceUsingEureka] nextServerInfo.getPort()-1935
2014-07-10 11:02:54,620 DEBUG com.netflix.eureka.SampleEurekaClient:78 [main] [sendRequestToServiceUsingEureka] nextServerInfo.getSecureVipAddress()-null
2014-07-10 11:02:54,620 DEBUG com.netflix.eureka.SampleEurekaClient:79 [main] [sendRequestToServiceUsingEureka] nextServerInfo.getStatusPageUrl()-http://defonds-win7:1935/Status
2014-07-10 11:02:54,620 DEBUG com.netflix.eureka.SampleEurekaClient:80 [main] [sendRequestToServiceUsingEureka] nextServerInfo.getVIPAddress()-sampleservice.mydomain.net
2014-07-10 11:02:54,620 DEBUG com.netflix.eureka.SampleEurekaClient:81 [main] [sendRequestToServiceUsingEureka] nextServerInfo.getLastDirtyTimestamp()-1404961230856
2014-07-10 11:02:54,620 DEBUG com.netflix.eureka.SampleEurekaClient:82 [main] [sendRequestToServiceUsingEureka] nextServerInfo.getHealthCheckUrls()-[http://defonds-win7:1935/healthcheck]
2014-07-10 11:02:54,621 DEBUG com.netflix.eureka.SampleEurekaClient:83 [main] [sendRequestToServiceUsingEureka] nextServerInfo.getStatus()-UP
        这些信息都和  http://serverIP:8080/eureka/v2/apps/  显示的 SAMPLESERVICE 实例的 各个属性一一对应。
         参考资料

• https://github.com/Netflix/eureka/tree/master/eureka-server/conf